Fire suppression systems are commonly used in commercial buildings for extinguishing fires. In one type of fire suppression system, a jet of liquid fire extinguishing agent, most commonly water from a water supply tank, is injected into a high velocity stream of pressurized inert gas from an inert gas storage tank as the inert gas passes through a supply pipe forming part of a network of distribution pipes communicating with a network of discharge nozzles mounted to the distal ends of the respective distribution pipes. Upon interaction of the high velocity stream of inert gas with the water jet, the water droplets in the water jet are atomized into a mist of very small or minute droplets, thereby forming a two-phase mixture of water mist droplets entrained in and carried by the inert gas stream. This two-phase mixture is distributed via the network of distribution pipes to the discharge nozzles that are operatively associated with the region to be protected. The discharge nozzles distribute the water mist droplets and inert gas over a desired area to flood that area with water mist droplets and inert gas to extinguish a fire in the protected region.
The inert gas commonly used in conventional inerting fire suppression systems is nitrogen, but argon, neon, helium, carbon dioxide or other chemically non-reactive gas, or mixtures of any two or more of these gases may be used. The inert gas suppresses fire within the protected region by diluting the oxygen content within the protected region and also increasing the heat capacity per mole of oxygen within the protected region thereby raising the overall heat capacity of the atmosphere within the protected volume. Due to the presence of the water droplets, the two-phase mixture of water mist droplets and inert gas has a higher overall local heat capacity than the inert gas alone. Consequently, the two-phase mixture of water mist droplets and inert gas will more effectively absorb heat from the flame to the point that the temperature of the gas within the vicinity of the flame sheath drops below a threshold temperature below which combustion can not be sustained. International Patent Application No. PCT/GB02/01495, published as International Publication WO02/078788, for example, discloses a fire and explosion suppression system of the type hereinbefore described.
In such two-phase fire suppression systems, non-homogenous distribution of water mist droplets within the two-phase mixture of water mist droplets and inert gas flowing through the fluid distribution network may occur. In long horizontally extending stretches of pipe within the fluid distribution network, the water mist droplets may not be evenly distributed in the gas flow. For example, the water mist droplets may have a tendency to concentrate in the lower half of the two-phase flow passing therethrough. When a pipe junction is reached whereat the two-phase is divided, it is desired that the water mist droplets be divided proportionally with the split of the inert gas flow as it passes from the inlet pipe to the junction into the two outlet pipes leading from the junction, thereby maintaining a constant mass flow ratio of liquid to gas. However, if the water mist droplets are not relatively uniformly distributed in the flow entering the junction, the water will not proportionally distribute between the respective inert flows discharging through the junction. Such a disproportionate distribution of water between the respective downstream streams could result in some spray nozzles being supplied with an excessive amount of water while other spray nozzles are under supplied.